Variable field device for process automation

ABSTRACT

In a field device for process automation, a reprogammable logic device is used, in order to achieve a high flexibility as regards hardware components.

FIELD OF THE INVENTION

The invention relates to a variable field device for process automation.

BACKGROUND OF THE INVENTION

In the technology of automation and process control, field devices areused in many cases in the flow path of an industrial process formeasuring (sensors) process variables or controlling (actuators)controlled variables.

Field devices for determining flow, fill status, pressure difference,temperature, etc. are generally known. For detecting the correspondingprocess variables mass, or volume, flow rate, fill level, pressure,temperature, etc., the field devices are most often arranged in theimmediate vicinity of the relevant process component.

The field devices deliver a measured signal, corresponding to the valueof the detected process variable. This measured signal is forwarded to acontrol unit (e.g. a programmable logic controller PLC, a control roomor process control system PCS). Normally, the process control isaccomplished by a control unit, where the measured signals of variousfield devices are evaluated and, on the basis of the evaluation, controlsignals are produced for the actuators, which control the course of theprocess.

In terms of an example of actuators, controllable valves can bementioned, which regulate the flow rate of a liquid or a gas in asection of a pipeline.

Signal transmission between field device and control unit can occur inanalog or digital form (e.g. current loop or digital data bus). Knowninternational standards for signal transmission include 4-20 milliamperecurrent loops, HART®, Profibus®, Foundation Fieldbus' or CAN-bus®.

The signal processing in the field device and the communication of thefield device with the control unit or other field devices is becomingalways more complex. To handle this, various hardware components withcorresponding software are being implemented in the field device. Thesoftware, which runs as a sequential program in a microprocessor, isnormally very flexible and can easily be replaced. The disadvantage inthe use of software is that the data processing proceeds sequentiallyand, for this reason, it is relatively slow.

Hardware components, in contrast, have a determined functionality, whichis hardwired in special chips, or integrated circuits (IC's). Examplesof such are ASIC's (Application Specific Integrated Circuits) or SMD's(Surface Mounted Devices). These devices are very application-specificand can, for example, execute an FFT (Fast Fourier Transformation),which is very calculations intensive, very quickly. The disadvantage ofthese hardware components is that they are only flexible to a slightdegree and normally must be replaced, in order to achieve a changing ofthe functionality.

The communication of the field device with a superordinated, evaluationunit occurs, likewise, over suitable hardware components partially stillin analog fashion or over a digital data bus.

Each field device is normally composed of various hardware components,which determine the functionality of the field device. Different fielddevices, for instance Coriolis mass flowmeters or electromagneticflowmeters (MID's), have entirely different hardware components. Evenfor one and the same field device, for example a Coriolis massflowmeter, the hardware components for communications can differ, forexample. For connection to a Profibus, a Profibus module is needed orconnection to a Foundation Fieldbus, a Foundation Fieldbus-module, etc.Depending on whether the field device is to deliver a frequency, pulseor current signal, corresponding hardware components have to beprovided.

This multiplicity of components means a considerable expense inmanufacture, since a multitude of hardware components has to beavailable.

A trend in the case of field devices is that they should be alwayscompacter. The components, especially the hardware components, are,therefore, always moving closer together on the circuit boards. A limithas almost been reached for this.

In order to assure the safety and the ability of a field device tofunction, the hardware components must be tested following thepopulating of the circuit boards. For test strategies to this point intime, a multitude of test pads are provided on the underside of thecircuit board. These pads can be contacted using a so-called bed ofnails. In this case, only certain circuit parts can be tested inisolation.

If, in the field, a Coriolis mass flowmeter is to be replaced by anelectromagnetic flow meter, it is presently necessary to replace theentire field device.

SUMMARY OF THE INVENTION

An object of the invention is to provide a variable field device forprocess automation. It should not display the above-describeddisadvantages, it should be flexible, have a compact form ofconstruction, be made of few parts, exhibit a high degree of safety andreliability, and simultaneously have a favorable cost and be easilymanufacturable.

This object is achieved by a variable field device for processautomation including: a sensor module SM for measured value detection; asigned processing module SPM connected to the sensor module SM; aprocessor module PM, connected to a communication module CU forconnection of the field device with a superordinated control-evaluationunit, wherein the signal processing unit SPM and the processor module PMare provided in the form of a reprogrammable logic device LD.

An essential idea of the invention is that various modules of the fielddevice are in the form of reprogrammable chips. Reprogrammable logicdevices are very flexible and can be configured simply such that theycan serve in the capacity of various hardware components.

Advantageous further developments of the invention are given in thedependent claims.

The invention will now be explained in greater detail on the basis of anexample of an embodiment presented in the drawing, the figures of whichshow as follows:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a data bus system in schematic presentation;

FIG. 2 is a schematic presentation of a conventional field device havingvarious hardware components;

FIG. 3 is a schematic presentation of a field device of the invention;

FIG. 4 is a schematic presentation of a reprogrammable logic device withflash memory; and

FIG. 5 is a schematic presentation of a logic device associated withmemory and loading controller.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows a data bus system DBS including a plurality of fielddevices and a process control system PCS. The field devices includevarious sensors S1, S2, S3 and actuators A1, A2. The data busparticipants (field devices and process control system) are connectedwith one another via a data bus DB.

The process control system is usually located in a control room, fromwhich the entire process control occurs. The sensors S1, S2, S3 and theactuators A1, A2 are in the field, i.e. located at the individualprocess components (tank, filling equipment, pipeline, etc.). Thesensors S1, S2, and S3 detect, for example, the process variablestemperature, pressure or flow rate at the particular process componentswhere they are located. The actuators A1 and A2, as valves, control theflow rate of a liquid or gas in a section of pipeline.

Data communication between process control system PCS, the sensors S1,S2, S3 and the actuators A1, A2 occurs in known manner according tointernationally standardized transmission technologies (RS435, IEC1158)by means of special protocols (e.g. Profibus, Foundation Fieldbus,CAN-Bus).

FIG. 2 shows a field device in the form of a typical sensor S1. SensorS1 includes a measurement transducer MT, which is connected with asensor unit SU. The sensor unit SU is followed by a digital signalprocessor DSP. The digital signal processor is connected with a systemprocessor MP. The system processor MP is connected via a communicationsunit CU with the data bus DB. Furthermore, the system processor MP isconnected with an analog unit AU, which has a plurality of inputs,outputs I/O. Serving for display of the measurement value and for manualinput is a display and operating unit DO, which is likewise connectedwith the system processor MP. The power supply of the sensor S1 is caredfor by a power supply unit PS, which is connected to the varioushardware components of the sensor S1, as indicated by the dashed lines.Power supply can occur externally or over the data bus DB.

The digital signal processor DSP and the system processor MP are eachconnected with watchdogs W1, W2 and EEPROM memories E1, E2.

The measurement transducer MT serves for detecting the process variablefor which it is intended and is based on, for example, atemperature-sensitive resistance or a pressure-sensitive piezo-elementor two coils, which detect the tube oscillation of a Coriolis massflowmeter. The analog signals of the measurement transducer MT arechanged in the sensor unit SU into digital signals and further processedin the digital signal processor DSP and fed to the system processor MPas measured value. The system processor MP controls the entire sensorS1. Connection to the data bus DB occurs via the communications unit CU.The communications unit CU reads telegrams on the data bus DB and itselfwrites data onto the data bus DB. It supports all transmitting andreceiving functions of the particular transmission technology which hasbeen chosen for the application.

In principle, every field device has a sensor module SM, which includesthe measurement transducer MT and the sensor unit SU, a signalprocessing module SPM, which can be e.g. the digital signal processorDSP, a processor module PM, which is essentially the system processorMP, and a communications module CM, which is either the communicationsunit CU and/or the analog unit AU.

FIG. 3 shows a first example of an embodiment of the sensor S1 of theinvention. FIG. 3 essentially corresponds to FIG. 2, with the differencethat the digital signal processor DSP and the system processor MP,including the watchdogs W1, W2 and the EEPROM's E1, E2 are replaced by alogic device LD. The logic device LD is additionally connected with apermanent memory SP (flash memory) and a loading, or booting, controllerLC.

FIG. 4 shows a further example of an embodiment. Here, the logic deviceLD includes not only the digital signal processor DSP and systemprocessor MP, but also parts of the display of the operating unit DO, aswell as the communications unit CU and parts of the analog unit AU andthe sensor unit SU. In the case of this example of an embodiment, thelogic device LD includes all digitally operating components of thesensor S. The outputs of the logic device LD serve only for activatingthe analog components of the sensor S1.

The logic device LD is a reconfigurable logic device, such as thatavailable from the firm Altera under the mark Excalibur.

FIG. 5 shows the configuring of the logic device LD in greater detail.The memory SP is divided into two memory ranges A and B. Memory range Acontains a description of the hardware of the logic device LD, whilememory range B contains the sequential program for the embeddedcontroller. On system start, the hardware of the logic device LD isconfigured with the help of the loading controller LC. At least oneembedded processor EP, one memory M and one logic L are configuredthereby. Once the hardware of the logic device is configured, thesequential program for the embedded controller is loaded into the memoryM.

This procedure brings-out an essential advantage of the sensor of theinvention, that, on system-start, both hardware and software can beconfigured in any desired fashion and matched thereby to the particulardemands of the application.

In the industry, such logic devices are also designated as SOPC, orsystem-on-a-programmable-chip. By using a reconfigurable logic deviceLD, a Coriolis mass flowmeter can easily be replaced by anelectromagnetic mass flowmeter MID, or any other field device. Necessaryto do this is only the appropriate reconfiguring of the logic device LDat system-start by new memory information in the memory ranges A and B.

As shown in FIG. 4, parts of the communication module can also beintegrated into the logic device LD. In this way, a sensor designed forthe HART protocol can easily be transformed into a sensor suited forProfibus' or FF. For this, only the appropriate region of the logicdevice LD must be configured at system-start.

By using a reconfigurable logic device LD, the parts multiplicityburdening the manufacture of a field device is considerably reduced. Afurther advantage offered by the field device of the invention is thatnew test strategies are possible. In principle, any areas, i.e.functionalities, of the logic device LD can be isolated and monitored.To do this, the logic device needs only to be correspondinglyconfigured, and the signals accessed at, and fed to, appropriate testpoints.

With the aid of reconfigurable logic devices, it is possible toconfigure hardware components, and, consequently, to change thefunctionality and behavior easily. The hardware components can, in thisway, be adapted to various tasks and functionalities. Inputs andoutputs, I/O's, can be easily defined. Especially, it is possibletherewith to define and amend function blocks, e.g. Flexible FunctionBlocks (Foundation Fieldbus Organization), or Profibus' function blocks(Profibus' Organization) easily with respect both to hardware andsoftware. The function block (Flexible Function Block or ProfibusR) isloaded into the reconfigurable logic device and generates its I/O'sitself. In this way, a logic device LD can be used for variousfunctionalities, just by loading the corresponding function blocks.

An essential idea of the invention is that use of a reconfigurable logicdevice makes it possible to embody field devices flexibly over a widerange of applications. The invention is, of course, not limited to justthe area of field devices, but, instead, can be used also for sensorsand actuators appropriate, for instance, in the field of motor vehiclemanufacture.

1. A variable field device for process automation, including: asuperordinated control-evaluation unit; a sensor module SM formeasured-value detection of a process variable in an application; asignal processing module SPM connected to said sensor module SM; acommunication module CU; and a processor module PM, which is connectedwith said communications module CU for connection of the field devicewith said superordinated control-evaluation unit, wherein: said signalprocessing module SPM and said processor module PM are provided in theform of a reprogrammable logic device LD; and at system start, bothhardware and software are configured on said reprogrammable logic deviceLD in a desired fashion thereby matching the particular demands of theapplication of said sensor module SM.
 2. The variable field device asclaimed in claim 1, wherein: said reprogrammable logic device LDincludes parts of said communication module CU.
 3. The variable fielddevice as claimed in claim 1, wherein: said reprogrammable logic deviceincludes parts of said sensor module SM.
 4. The variable field device asclaimed in claim 1, wherein: said reprogammable logic device LD includesall digitally working components of said sensor module SM.
 5. Thevariable field device as claimed in claim 1, wherein: saidreprogrammable logic device LD includes at least one embedded processorEP, one memory M and one logic L.
 6. The variable field device asclaimed in claim 1, wherein: said reprogrammable logic device LD serves,in operation, as an SOPC-system (system-on-a-programmable-chip).
 7. Thevariable field device as claimed in claim 1, wherein: saidcommunications module CU has a data bus interface, which comprise oneof: Profibus®, Foundation Fieldbus®, and CAN®-Bus.
 8. The variable fielddevice as claimed in claim 1, wherein: said communications module CU hasa data bus interface which comprises one of: one or more analoginputs/outputs I/O's, which are one of: frequency output, and pulseoutput.
 9. The variable field device as claimed in claim 1, wherein: afunction block is loaded into said reprogrammable logic device LD. 10.The variable field device as claimed in claim 9, wherein: said functionblock is a Flexible Function Block of one of: Foundation Fieldbus; and aProfibus function block.